A TailSok is a very practical, effective addition that provides a lot of bang for the buck. They are designed to be light, easy to use fairings that improve both speed and rider visibility. It's true that they aren't the most aerodynamic thing you can do for your bike, as the most aerodynamic things are also inherently less practical. Instead, the TailSok system is designed to be both very effective and very practical—something everyone can live with and benefit from. The speed improvement due to a TailSok is typically in the 4 to 8% range, depending on the bike and the rider. And, speed aside, the visibility improvement alone is worth getting one. All of this for around the weight of a waterbottle! You will be amazed. 


1. What's a TailSok? 

A TailSok is a simple, lightweight rear fairing that streamlines the airflow off the back of your seat. It uses a Lycra "sock" stretched over a frame. The sock has a mesh panel that goes over the front of the seat. TailSoks are a simple and effective way to add speed and visibility. As it turns out, smoothing the airflow behind you is an important part of being aerodynamic. Smoothing airflow at the front is obvious, but smoothing it at the rear is also critically important. 

2. What's special about this frame? 

This frame is unique in how adaptable and adjustable it is. You can attach it to nearly any bike and adjust it for nearly any combination of seat and sock shape. The attachment and adjustment are very easy to do. For the best aerodynamics, it's important the sock is stretched properly in all directions, so it's smooth and tight and creates the ideal shape. This frame lets you do that. 

3. Is it difficult to attach? 

It's very easy to attach. It attaches to your bike in 4 places, using Cateye brand plastic band clamps. We use Cateye clamps because they are well made and are available in 1/8 inch increments from 1/2 inch to 1-1/4 inch. All you need to know is the diameter of where you are attaching. If you have a bike that doesn't have a tube to attach to, other arrangements are possible. The frame attaches with 5mm bolts, so something like a small L bracket with holes for a 5mm bolt is all you would need. We make stainless steel ones for use with Accessory Mounting; contact us if you'd like more information. In most cases, you can attach the frame to your bike with the 4 Cateye clamps. 
Usually, the frame will attach at the top and the bottom of the seat back angle adjustment stays. Measure the size at the top and the bottom, and you're all set. 

4. Do I have to leave it on all the time? 

No. It's easy enough to pop it off and put it back on. 4 bolts is all it takes. 

5. How much faster will I be? 

That depends on a lot of things, but in most cases it's 1 gear higher for the same effort, sometimes 2 gears. In coastdown tests, it's usually in the 4-8% range. 

6. Do I need a light mount? 

If you are only racing, no. If you have other good places on your bike to put a rear light, you wouldn't need an additional mount on the frame. The optional light mount lets you put a rear light at the back of the sock where it's most visible. It also has a spot to mount an inside light. A flashing white light illuminating the inside of the sock creates a very attention getting effect. 

7. Where do I get a sock? 

We sell them. Some people make their own. Some people order custom things direct from Free Form Fashions, who makes the socks for us. 


by Patrick Franz

It does appear that there is a wide range of rider experiences out there when it comes to fairings of any kind. Heck, when it comes to bikes of any kind! 

A couple years back, we did a fairly extensive test of our TailSok rear fairings with the help of folks from the Oregon Human Powered Vehicles Association. The goal was to get some real data, and we pretty much succeeded in that. It turns out that testing is a complicated thing. 

The test we did was a coastdown test, no pedalling, and we recorded the max speed. We had a long enough, steady enough hill that we were sure we reached terminal velocity. We got a lot of data, some of which was very useful and some of which was not. 

Some of the runs were with full body socks, and some runs were orphaned in that we didn't get the second configuration tested in time. A few runs were invalidated because people changed jackets or tires. The hill was steeper than we wanted, but was the only one of about 20 candidate locations scouted that met the criteria for steadiness of grade, course safety, and proximity to Portland. 

Here's what we did: we found a long, steady hill with good pavement and little traffic (steady 6% grade for 2 miles). We invited people from the Oregon Human Powered Vehicles Association to come and test their bikes. People coasted down the hill, and we recorded their max speeds in various configurations of fairing/no fairing. We went for at least 3 runs per person/bike/configuration. Two vehicles ferried people back to the top. We got in about 68 runs in 4 hours. 

We had three course marshals, a bike safety officer, a photographer, and a data clerk. There was quite a turnout, and everyone had a good time and vowed to come back. The OHPV gang is a great bunch! 

In amongst the data, we got 22 directly comparable tailsock off/tailsock on runs. Here are the numbers: 

  • Average of 22 runs, 7 bikes, without sock: 39.67mph
  • Average of 22 runs, 7 bikes, with sock: 42.00mph
  • Difference: +2.33mph for sock

This is from 7 different bikes, with an equal number of runs with/without from each bike. Most bikes had 3 runs each; one bike had 4 runs each. Bikes included a Django, a Giro 26 (with front fairing), a Corsa, an Aero, a Zox clone, and a couple of Easy Racers. 

The improvement for each of the 7 bikes ranged from +1.23 to +3.83 mph. 

We learned a lot, and, next time, we plan to do some things a little differently. For one, we'd like to find a course with a 3-4% grade so max speeds won't be almost 2x typical cruising speed. In subsequent tests on a different hill, the speed percentages held true. It was good to have data at 20mph instead of 40, but we'd like to have tested more riders there. Second, we'd like to test fewer bikes but do more runs per bike. Third, we'd like to record not only max speed, but the overall time as well. We were going to do this, but the radios didn't show up. The other thing we'd like to record is bike+rider weight. We also plan to have one bike that goes down frequently without changing configuration, to serve as a control. 

We'd really like to understand why some bikes/riders show big improvements and others only small improvements. One thing everyone does find is that the socks are highly visible, particularly the neon ones. We get at least as many comments about visibility as we do speed.


  • The frame has 4 adjustable extension aluminum legs. The legs attach to your bike with Cateye brand plastic band clamps. Cateye clamps are the best plastic clamp we know of. They come in 1/8 inch increments from 1/2 inch to 1-1/4 inch. The four legs are held together with an industrial urethane tip. The legs are made extra long so you are guaranteed to have as much adjustment range as you will ever need. They come with end caps, so that after installation, you can remove any extra and the ends will be covered.
  • Weight, at full extension: 630g. In most configurations, you should be able to cut this back to 350g or so.
  • Max Extension: 43 inches (109cm). Typically, the back end of the sock is about 25 inches (63cm) or so from the top of the seat. This gives plenty of extra for bikes where the attachment point is below and ahead of the top of the seat.
  • The frame usually attaches at the top and bottom of your seatback angle adjustment stays. Measure the diameter at the top and the bottom and you're all set. If you don't have seatback adjustment stays, you can attach to any tube on the back of your seat. If you don't have any tubes on the back of your seat, it's usually pretty easy to adapt a bracket to the back of the seat. Contact Us if you have any questions about mounting.
  • The legs of the frame are aluminum rods 5/16 inch (8mm) in diameter. The original TailSok frames we used to make were made with 5/16 inch tubing, but the cost on the tubing went to over $7.00/foot (in 1000 foot quantities!). Since there are 4 legs, each nearly 4 feet long, this made the frames too expensive to produce. The rods are easily cut with a hacksaw or tubing cutter. We provide vinyl end caps to cover any roughness.
  • The length adjuster clamps grip two rods at once and allow you to slide them past each other. The clamps look lightweight, but they are much stronger than you might expect. You can position the clamps right up to the end of the rods and they will still grip 100% securely. They are precision machined to match the rods and they lock the rods in very nicely.
  • The clips for tensioning the bottom of the Sock attach with a special Velcro band. They are usually attached to the chainstays near the rear dropouts. They can be used on tubes from 1/2 inch (12mm) to 1-1/8 inch (28.6mm) in diameter. If you have an Easy Racers bike, the usual thing is to hook the lower tabs on the Sock around the ends of the seatback adjustment rods. In this case, you don't need the strap on clips. For most other bikes, you'll need the strap on clips.
  • Installation is straightforward. First, locate where to clamp things on. Usually, this will be at the top and the bottom of the seat back angle adjustment stays. Next, attach the ends of the frame there, then adjust the position of the support tip. Lock down the adjustment clamps, and you're set. If you're using the Velcro strap clips to tension the bottom of the sock, strap them around the chainstays, put the sock on, and you're ready to go.
  • Because this system is so versatile, it can be used out of the box on nearly any bike. Be sure to measure at the top and bottom of your seatback adjustment stays to order the right size clamps for them. If you don't have seatback adjustment stays, you can attach to any tube on the back of your seat. If you don't have any tubes on the back of your seat, it's usually pretty easy to adapt a bracket to the back of the seat. Contact us if you have any questions about mounting.
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